1) Field of Invention
This invention relates to a phase shift mask capable of transferring patterns with an improved resolution upon placing phase differentials between exposure light rays that pass through the mask, a phase shift mask blank as a material for the phase shift mask, and a manufacturing method for the phase shift mask, and, more particularly, to a half tone type phase shift mask, and blank and manufacturing method for the mask.
2) Related Arts
It has been recently turned out that mere increase of numerical aperture of exposure apparatus"" lens or mere reduction of wavelength of exposure apparatus"" beam cannot improve practical resolution for lithography, since two key factors, rendition of higher resolution and assurance of depth of focus, required for lithography are in a trade-off relation.
Under this situation, phase shift lithography is getting attentions as lithography of the next generation. The phase shift lithography is a method to improve photo lithography""s resolution by changing only masks without changing any optical system, and can grossly improve the resolution in using interference between transmission light rays upon placing phase differentials between exposure light rays that pass through the photo masks. Such a phase shift mask is a mask in common possession of light intensity information and phase information, and is categorized in several types such as, so-called Levenson, auxiliary pattern, self-alignment (edge enhancement), or the like. Those phase shift masks have more complicated structures in comparison with those of conventional photo masks which possess only light intensity information, and require a higher level of technology in regard of manufacturing.
As one of such phase shift masks, a phase shift mask referred as to a half tone type phase shift mask has been developed these days. In such a half tone phase shift mask, its light translucent portion (photo semi-transmission portion) produces a light shield function in which exposure light is substantially shielded and a phase shift function in which phase of light is shifted (ordinarily reversed), and therefore, the half tone phase shift mask, without necessity to form separately a light-shield film pattern and a phase shift film pattern, has a feature that the structure of the mask can be made simple and that a manufacturing process of the mask can become easy.
A typical conventional half tone type phase shift mask is shown in FIG. 1. The half tone type phase shift mask has on a transparent substrate 1 a mask pattern, which is as shown in FIG. 1(a) composed of a light transmitting portion (a photo transmission portion) (exposure areas of the transparent substrate) 2 through which light with intensity capable of substantially contributing to the exposure process passes, and a light translucent portion (light shield and phase shift portion) 3 through which light with intensity unable to substantially contribute to the exposure process passes. The phase of light passing through the light translucent portion is shifted, and the phase of the light that has passed through the light translucent portion thereby enters a substantially reverse relation with the phase of light that has passed through the light transmitting portion (see FIG. 1(b)); lights passing through boundaries or their vicinities between the light translucent portion and the light transmitting portion and diffracting as to encroach one another due to diffraction phenomenon behave to cancel one another; the light thereby improves the contrast at the boundaries, or the resolution, while the light intensity around the boundaries are nearly nullified.
Meanwhile, the light translucent portion for the half tone type phase shift mask described above must have the optimum values for the transmittancy or transmission rate and the phase shift amount. It has been known that such optimum values in a phase shift mask can be realized by a single layer of the light transmitting portion. Such a phase shift mask has a light transmitting portion made by a thin film made of, as a material or materials essentially, metals such as molybdenum, silicon, and oxygen. They are such as molybdenum silicides, more specifically, oxides of molybdenum silicon (xe2x80x9cMoSiO system materialxe2x80x9d), or nitride oxides of molybdenum silicon (xe2x80x9cMoSiON system materialxe2x80x9d). According to those materials, transmittancy can be controlled by selecting the containing amount of the oxygen or the nitrogen and oxygen, while the thickness of the thin film can control the phase shift amount. When formed of those materials, the light transmitting portion can be structured by a single layer film made of a single kind material, thereby simplifying the film formation process in comparison with a case where it is made of multilayer film made of multiple materials, and thereby simplifying the manufacturing process since a single etchant can be used.
However, the molybdenum silicide film or the molybdenum silicide nitride oxide film, as elements composing the light translucent portion of the phase shift mask is weak against acid, such as sulfuric acid, used for primer or rinse fluid for rinsing during mask manufacturing or when masks are used. In particular, where the transmission rate and phase shift amount of the light translucent portion is set for KrF excimer laser beam (248 nanometers), the attenuation constant (K) must be small, and to realize a small attenuation constant, degree of oxidation or nitriding oxidation has to be increased sufficiently. If the oxidation degree is so increased, acid resistance of the light translucent portion is significantly lowered, thereby raising a problem that the transmission rate and phase shift amount thus set may be deviated.
While a film for phase shift mask blanks is formed, oxide tends to deposit on target surfaces, especially on non-erosion areas as the degree of oxidation or nitriding oxidation increases, and makes electrical discharge of the film unstable. Consequently, the transmission rate and phase shift amount is poorly controlled, thereby raising a problem that the blanks are formed with defects. Moreover, since the relationship between the composition of the film and film characteristics such as acid resistance, photo resistance, conductivity, deflection rate (thickness), transmission rate, selectivity of etching, etc. remains unsolved, the optimum film characteristics cannot be obtained in consideration of the manufacturing process or the likes even if the required optimum values for both of the transmission rate and the phase shift amount are obtained at the stage of blanks, and therefore those values are deviated from the designed or set values through experiencing the manufacturing process, resulting in disability to form the optimum phase shift masks.
It is an object of the invention to provide a phase shift mask having a light translucent portion of good film characteristics such as acid resistance, photo resistance (durabillity against light (UV irradiation)), conductivity, deflection rate (thickness), transmission rate, phase shift amount, selectivity of etching, etc. and a blank for the phase shift mask.
It is another object of the invention to provide a manufacturing method for the blank for the phase shift mask with a light translucent portion of excellent film characteristics.
In one form of the invention, a phase shift mask for exposure of a very fine pattern, has a transparent substrate and a mask pattern formed on the transparent substrate. The mask pattern has a light transmitting portion transmitting light having intensity substantially contributing to the exposure and a light translucent portion transmitting light having intensity substantially not contributing to the exposure. The light translucent portion shifts a phase of the light having passed through the light translucent portion to cancel, by rendering the phase of the light having transmitted through the light translucent portion differentiated from a phase of the light having transmitted through the light transmitting portion, intensity of light transmitted around through a boundary located between the light translucent portion and the light transmitting portion for an improvement of a contrast at the boundary. The light translucent portion is formed of a thin film made of a material including essentially nitrogen, metal, and silicon whose containing rate is set at thirty atomic percent or greater and at sixty atomic percent or less.
In another form of the invention, the phase shift mask has a specific range of sheet resistance in lieu of the specific range of the containing rate of silicon. In this phase shift mask, a sheet resistance of the substrate on which the thin film is formed is set at one kilo ohm per square or greater and at one point five mega ohm per square or less.
According to a preferred embodiment of the invention, the ratio of the metal to the silicon is one to one point five or greater and one to six or less. The containing rate of the nitrogen may be set at thirty atomic percent or greater and at sixty atomic percent or less, and preferably, the containing rate of the nitrogen is set higher than the containing rate of the silicon. The metal for the phase shift mask of the invention can be made of, but not limited to molybdenum.
According to another preferred embodiment of the invention, a phase shift mask blank is manufactured by preparing a target containing silicon of seventy to ninety mole percent and metal, and sputtering atoms from the target in an atmosphere including nitrogen to form a phase shift layer including nitrogen, metal, and silicon. Such a phase shift mask blank may be formed with a transparent substrate, and a thin film made of a material essentially including nitrogen, metal, and silicon.